tests: fixed "ARP replies for SNAT external ips" #2061

Job	Run time
osx clang --disable-ssl	4m 54s
linux gcc --disable-ssl	4m 24s
linux clang --disable-ssl	4m 28s
linux gcc test -500	23m 28s
linux gcc test 501-1000	14m 26s
linux gcc test 1001-	8m 7s
linux clang test sanitizers -300	18m 48s
linux clang test sanitizers 301-600	25m 27s
linux clang test sanitizers 601-900	15m 27s
linux clang test sanitizers 901-1200	14m 28s
linux clang test sanitizers 1201-	9m 24s
linux gcc test -ljemalloc -500	24m 43s
linux gcc test -ljemalloc 501-1000	14m 35s
linux gcc test -ljemalloc 1001-	10m 16s
linux clang test -ljemalloc -500	24m 33s
linux clang test -ljemalloc 501-1000	15m 39s
linux clang test -ljemalloc 1001-	10m 22s
linux gcc system-test -100	15m 50s
linux gcc system-test 101-200	22m 29s
linux gcc system-test 201-	18m 22s
linux clang system-test sanitizers -100	19m 10s
linux clang system-test sanitizers 101-200	24m 4s
linux clang system-test sanitizers 201-	20m 18s
linux gcc m32 --disable-ssl	5m 5s
	6h 8m 47s

Provide feedback